Steve Harmison's chances of forcing his way into England's Ashes attack have been enhanced by his demolition of Nottinghamshire at Trent Bridge. Harmison's intimidating performance under glowering skies brought him 6-20, leaving Notts on the verge of an innings defeat on the final day and Durham about to strengthen their position at the top of the championship with a fifth win in six matches.

Harmison, on the brink of recording his best championship figures for Durham, now has 49 first-class wickets this summer at about 18 runs apiece, but if that will swell the ranks of those advocating an Ashes return for this most mercurial of fast bowlers, his rewards also owed much to vacillating Nottinghamshire's batting in the face of his physical threat.

There is no doubt that Harmison has had an impressive match since England released him on Thursday morning and he drove 110 miles north to join Durham on the second afternoon of their championship match. His immediate retort on the second day – an eight-over spell that conceded a solitary single – emphasised that his mind was right on the job.

On the third day, his assault carried more potency and left Notts increasingly disheartened. Three batsmen surrendered their wicket weakly and those who did not, Bilal Shafayat and Chris Read, both departed to catches by the wicketkeeper Phil Mustard with a show of grievance.

Shafayat, a central figure in England's timewasting antics in the final moments of the first Test, left the outfield even more slowly than he had when he was England 12th man in Cardiff.

Notts, following on 185 behind, disintegrated to 68-8 by lunch, but Harmison, as insistently as he bowled, as menacing as his lofty frame can seem on a pitch sharpened under glowering skies, was the beneficiary of Notts' lack of character.

Samit Patel slapped a high, wide one to cover in a manner that suggested his England omission because of weight and fitness issues might yet send his career into decline; Ally Brown hooked prematurely, top-edged and fell to an eager catch at long leg by Mark Davies; and Andrew Adams's step-away to the leg-side to carve Harmison to point was simply scandalous, a dismissal so lacking in pride that the Notts members should have congregated outside the pavilion to boo him off.

It all added up to a satisfying morning for Harmison, whose warm-up in the nets had caught the eye as he walked out to the nets in gloves and a beanie hat on a damp, sultry morning in temperatures of 21C.

Rain then fell, although in one brief interlude he added a sixth wicket – Ryan Sidebottom's flinching defence no match for him. As the weather turned sour again, Notts ended the day 106 runs behind, their title aspirations in tatters. The Met Office forecast suggests that they will not be spared the last rites.

The message was plain: Harmison is in rhythm, committed to Durham's championship challenge and wants to add to his 61 Test caps. If England look in his direction again they are likely to find a fast bowler in good shape. There might not be a bouncy pitch until the final Test at The Oval, but if there is a chance of a jubilant Test farewell for his old mate Andrew Flintoff, Harmison will want to be part of it.